Reports of sexual misconduct by prison staff members with federal inmates doubled over the past eight years, and government watchdogs called Thursday for more training and sensitivity to combat the growing problem.

After studying hundreds of cases of alleged sexual assault, Justice Department Inspector General Glenn A. Fine concluded that the response of the Federal Bureau of Prisons has been "mixed" despite changes in the law and vocal efforts to crack down on misconduct.

The issue underscores broader concerns about security and law-breaking inside the nation's 93 federal prison sites, all but one of which has had allegations of sexual abuse by staff members since 2001.

"Sexual abuse of inmates in BOP facilities has severe consequences for victims and undermines the safety and security of federal prisons," Fine said in a statement. "We believe the department should take additional steps to further improve its efforts to address this serious problem."

In one incident highlighted in the report, a male correctional officer agreed to pay a female inmate with whom he had sex to arrange for his wife's murder. Of the 90 staff members prosecuted for sexual abuse of inmates, nearly 40 percent were also convicted of other crimes, authorities said.

Investigators underscored the damaging effect such episodes can have on the overall security within a prison. One operations officer abandoned his post several times to have sex with a female inmate. Another manager scrubbed the prison database to remove unflattering information about a prisoner and entered a phony request that allowed the inmate to transfer from a high-security facility to a less secure one.

In what the inspector general called a "particularly egregious case," a ring of corrections officers provided gifts to prisoners in return for sex, allowed the inmates to leave their cells and gave prison employees keys to offices so they could engage in sex with prisoners. To prevent detection, the officers allegedly intimidated prisoners to keep them from cooperating with investigators. Six of the officers were indicted in 2006, and when agents went to the prison to arrest them, one correctional officer pulled a smuggled gun and shot at random, wounding a prison lieutenant and killing inspector general agent William Sentner III.

A congressionally chartered panel earlier this year urged broad reforms within the nation's prisons to crack down on sexual abuse and misconduct, particularly involving staff members who wield an unusual amount of control over inmates.

It is a crime for a prison staff member to engage in any sexual activity with an inmate, and consent by the inmate does not matter under the law because of the imbalance of power in the relationship.

The Prison Rape Elimination Act of 2003 mandates that prison officials make prevention of sexual abuse in prisons, jails and cellblocks a top priority. The Federal Bureau of Prisons manages 115 facilities and houses 171,000 inmates.

At the same time, serious challenges continue to hamper the ability to prosecute such cases, the inspector general said, citing a lack of physical evidence, delayed reporting of the allegations by inmates and a lack of cooperation inside prison walls.

Fine urged the Justice Department, the Bureau of Prisons and the U.S. Marshals Service to step up their outreach to prosecutors and to reconsider policies in some prison facilities that isolate inmates or transfer them after they raise allegations of sexual misconduct by corrections officers and other members of the prison staff.

Since a change in the law in 2006, the percentage of cases that assistant U.S. attorneys accepted for prosecution has risen by more than 12 percent. In the cases in which criminal charges were filed, 83 out of 90 resulted in convictions. The vast majority of the penalties, however, resulted in sentences of less than one year of prison time under both the older and newer laws.

Female staff members were less likely to receive prison sentences after being convicted of sex crimes against inmates, but allegations about women staff members rose in "numbers disproportionate to their representation in the BOP workforce," the inspector general's report said.

Overall, allegations of sexual abuse by staff members of both sexes more than doubled over the past eight years, at a rate higher than both the growth in prison population and in BOP staff.

Harley G. Lappin, director of the Bureau of Prisons, pointed out in a letter that prison officials attribute the rise in allegations "to our efforts to educate and encourage reporting of these incidents" by inmates and other prison staff members.